UFC 3-570-06
JANUARY 31 2003
Figure 7-35. IR Drop Test Span, Direction Of Current Flow
-4 .3 2 m V
V oltm et er
-
+
P ip elin e or c ab le
+ 4 .3 2 m V
V oltm et er
-
+
P ip elin e or c ab le
7-13.3
Resistance of the Pipeline. The resistance of the pipeline can be
calculated if the distance of the test span is known and the size of the pipeline is
accurately known. Resistance joints or insulators cannot be present on the pipeline in
the test span. Variations in temperature will adversely affect the accuracy of these
calculations.
7-13.3.1 The mV IR drop is measured by using a voltmeter on the mV scale as shown
in Figure 7-35. Following all polarities in Figure 7-35, connect the meter to the inside
circuit and record the measurement. Polarity is important for correct determination of
the direction of the current flow in the pipeline or cable during subsequent test
procedures.
7-13.3.2 The resistance is estimated using Table 7-3. The resistance is given in
millionths of an ohm (0.000001 ohms) per linear foot of pipeline. This resistance value
must be multiplied by the number of feet in the test span (distance in feet of the pipeline
between the actual connection points of the test station leads to the pipeline).
7-52
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